The game remains equal after this move, but it's not easy to play with Black.
18. d4c5  18... d5d4 A very difficult choice. 19. c3c4 Another tough choice, now for White. This move allows Black to equalize. 19... f6g5 an important move, attacking both the knight and the pawn on c5. 20. f1d1 The alternatives are no better.